Enabling Down Link Reception of System and Control Information From Intra-Frequency Neighbors Without Gaps in the Serving Cell in Evolved-UTRA Systems

ABSTRACT

Simplified communication between user equipment and a neighboring cell not the primary cell is achieved by restricting the transmission parameters, such as bandwidth, of the neighboring cell transmission and provision of a simplified secondary baseband processor in the user equipment.

CLAIM OF PRIORITY

This application claims priority under 35 U.S.C. 119(e)(1) to U.S.Provisional Application No. 60/895,633 filed Mar. 19, 2007.

TECHNICAL FIELD OF THE INVENTION

The technical field of this invention is wireless telephonecommunication, particularly Evolved-UMTS Radio Access (E-UTRA)communication.

BACKGROUND OF THE INVENTION

As wireless systems proliferate, the expanding user base and the demandfor new services necessitate the development of technologies capable ofmeeting users' ever increasing expectations. Users of mobiletelecommunications devices expect not only globally available reliablevoice communications but a variety of data services, such as email, textmessaging and internet access.

SUMMARY OF THE INVENTION

Reception of relevant down link (DL) transmissions in neighboring cellsby a mobile UE fully connected in a serving cell requires significantadditional circuitry if no structure is imposed on the DL transmissionsin Orthogonal Frequency Division Multiple Access (OFDMA) based E-UTRAsystems. This invention includes some structure and format for relevantDL transmissions to aid in dual reception with minimal implementationcomplexity.

This invention is an E-UTRA protocol such that UEs connected in a cellcan decode some of the transmissions from neighboring cells' withoutgaps and with minimum implementation complexity. This invention issimilar to a synchronization channel and a broadcast channel (BCH) whichare limited to 1.25 MHz bandwidth, the first block in dynamic-BCH(D-BCH) and random access channel (RACH) response messages 2 and 4 aretransmitted in bandwidth limited regions. This invention also includesseparately encoding the allocations for the first D-BCH block and theRACH responses. These are the foremost allocations in the L1-L2 controlchannel.

This invention provides a minimal protocol performance compromise forsignificant reduction in implementation complexity. This inventionenables DL reception in neighbors without gaps in the current cell andwith minimal additional circuitry compared to simply receiving one cell.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of this invention are illustrated in thedrawings, in which:

FIG. 1 is a diagram of a communication system of the present inventionhaving three cells;

FIG. 2 is a block diagram of a transmitter of the present invention;

FIG. 3 is a block diagram of a receiver of the present invention;

FIG. 4 is a diagram showing a procedure for establishing communicationsbetween user equipment (UE) and a base station (Node B);

FIG. 5 is a flow chart illustrating operation of this invention; and

FIG. 6 is a simplified block diagram of user equipment adapted accordingto this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

FIG. 1 shows an exemplary wireless telecommunications network 100. Theillustrative telecommunications network includes base stations 101, 102and 103, though in operation, a telecommunications network necessarilyincludes many more base stations. Each of base stations 101, 102 and 103are operable over corresponding coverage areas 104, 105 and 106. Eachbase station's coverage area is further divided into cells. In theillustrated network, each base station's coverage area is divided intothree cells. Handset or other user equipment (UE) 109 is shown in Cell A108. Cell A 108 is within coverage area 104 of base station 101. Basestation 101 transmits to and receives transmissions from UE 109. As UE109 moves out of Cell A 108 and into Cell B 107, UE 109 may be handedover to base station 102. Because UE 109 is synchronized with basestation 101, UE 109 can employ non-synchronized random access toinitiate handover to base station 102.

Non-synchronized UE 109 also employs non-synchronous random access torequest allocation of up-link 111 time or frequency or code resources.If UE 109 has data ready for transmission, which may be traffic data,measurements report, tracking area update, UE 109 can transmit a randomaccess signal on up-link 111. The random access signal notifies basestation 101 that UE 109 requires up-link resources to transmit the UE'sdata. Base station 101 responds by transmitting to UE 109 via down-link110, a message containing the parameters of the resources allocated forUE 109 up-link transmission along with a possible timing errorcorrection. After receiving the resource allocation and a possibletiming advance message transmitted on down-link 110 by base station 101,UE 109 optionally adjusts its transmit timing and transmits the data onup-link 111 employing the allotted resources during the prescribed timeinterval.

FIG. 2 is a block diagram of a wireless transmitter 200 of the presentinvention for transmitting a preamble 202 to a remote receiver. Thepreamble is preferably a CAZAC sequence for generating the random accesspreamble signal. CAZAC sequences are complex valued sequences withfollowing two properties: 1) Constant Amplitude (CA), and 2) Zero CyclicAutocorrelation (ZAC). Examples of CAZAC sequences include but are notlimited to: Chu Sequences; Frank-Zadoff Sequences; Zadoff-Chu (ZC)Sequences; and Generalized Chirp-Like (GCL) Sequences.

Zadoff-Chu (ZC) sequences are defined by:

a _(M)(k)=exp[j2π(M/N)[k(k+1)/2+qk]] for N odd

a _(M)(k)=exp[j2π(M/N)[k ²/2+qk]] for N even

where: N is the length of the sequence; M is the index of the root ZCsequence with M and N being relatively prime; q is any fixed integer;and k is the index of the sequence element ranging from 0 to N−1. Theseare representative examples of CAZAC sequences. An alternativeconvention for ZC definition replaces j in the above formula by −j.Either convention can be adopted. In the above formula, making N a primenumber maximizes the set of non-orthogonal root ZC sequences havingoptimal cross-correlation. When N is prime, there are (N−1) possiblechoices for M. Each such choice results in a distinct root ZC CAZACsequence. In this application the terms Zadoff-Chu, ZC and ZC CAZAC willbe used interchangeably. The term CAZAC denotes any CAZAC sequence, ZCor otherwise.

In a preferred embodiment of the invention, random access preamblesignal 202 is constructed from a CAZAC sequence, such as a ZC sequence.Additional modifications to the selected CAZAC sequence can be performedusing any of the following operations: multiplication by a complexconstant, Discrete Fourier Transform (DFT), inverse Discrete FourierTransform (IDFT), Fast Fourier Transform (FFT), inverse Fast FourierTransform (IFFT), cyclic shifting, zero padding, sequence blockrepetition, sequence truncation, sequence cyclic extension and others.In the preferred embodiment of the invention, UE 200 selects randomaccess preamble signal 202, by selecting a CAZAC sequence and optionallymodified as noted above. DFT circuit 204 receives the modified CAZACsequence to produce a frequency domain signal. Sub-carrier mappingcircuit 206 receives the frequency domain signal. Sub-carrier mappingcircuit maps the preamble to user selected tones. IDFT circuit 208 thenconverts the user selected tones to a time domain signal which issupplied to parallel-to-serial converter 210. The resulting preamble isoptionally repeated to achieve the desired duration. Cyclic prefix (CP)circuit 214 adds a cyclic prefix to the preamble before transmission toa remote receiver.

FIG. 3 is a block diagram of an embodiment of a random access channelreceiver 300 of the present invention. CP removal circuit 302 removesthe cyclic prefix from the received random access signal.Serial-to-parallel converter 304 converts the resulting preamble into aparallel signal. DFT circuit 306 produces sub-carrier mapped tones fromthe parallel preamble components. Sub-carrier de-mapping circuit 308demaps the mapped tones. These demapped tones are equivalent to theoutput signal from DFT circuit 204 of transmitter 200 (FIG. 2).Parallel-to-serial circuit 310 converts the parallel demapped tones intoa serial data stream. Product circuit 312 receives this serial datastream and a reference root sequence from DFT circuit 320. Productcircuit 312 computes a tone by tone complex multiplication of demappedtones with the reference tones. Zero padding circuit 314 adds a numberof zeros necessary to produce a correct sequence length. IDFT circuit316 converts the multiplied frequency tones into time domain signals.These time domain signals include concatenated power delay profiles ofall cyclic shift replicas of the preamble root sequence. Energy detectorcircuit 318 detects the energy in the time domain signals. Thisidentifies the received preamble sequences by detecting the time of peakcorrelation between received random access preamble signals and thereference ZC root sequence.

FIG. 4 illustrates the procedure for establishing communications via theRACH between UE 109 constructed as illustrated in FIG. 2 and a Node B101 as illustrated in FIG. 3. The horizontal arrow of time 410illustrates the following sequence. Node B 101 periodically transmits abroadcast signal 400 within the cell having slot and frame timinginformation for UE 109. UE 109 selects an appropriate CAZAC sequence andproduces a preamble with appended cyclic prefix as described above. UE109 transmits this preamble 402 over the RACH to Node B 101. Node B 101identifies the preamble and responds with timing adjustments 404 tosynchronize communications and adjust for transmit delay. Oncesynchronized with Node B 101, UE 109 transmits communication resourcerequest 406. Alternatively, the communication resource request might beincluded as part of RACH signal 402. Node B 101 then transmitscommunication resources assignment 408 to UE 109. Synchronouscommunication can then begin over the primary user channel.

One important capability of UE 109 is the ability to receive and decodesimultaneously from multiple cells. This ability is important for makingmeasurements or reading selected data from neighboring cells whileremaining fully connected to the primary cell. Given the complexitiesand cost of additional circuitry within UE 109, including an additionalRF or an additional baseband receiver within UE 109 is not efficient.The majority of the time these additional circuits will not be used. Ifno additional circuitry than that required for the primary cellreception is provided, communication may still be possible with certainlimitations in protocol design. For example, in asynchronous networksgaps in connectivity with the primary cell is necessary to enable anyreception from neighboring cells. There are various reasons why UE 109may want to receive from neighboring cells, while maintaining fullcommunication with the primary cell. These reasons generally do notrequire UE 109 to be able to receive the neighboring cell transmissionsover the entire bandwidth with full reception capability as in theprimary cell. For example, UE 109 may only need to receive certainlimited channels such as broadcast channel (BCH) from the neighboringcells. Including additional circuitry in UE 109 for such limitedadditional reception may not be as prohibitive as additional circuitsfor full duplex reception. It is thus advantageous to design a protocolrequiring minimal complexity in UE 109 for such neighbor receptionwithout gaps in the reception from the primary cell.

This invention gives some structure to the various DL transmissions inthe protocol, so that UEs 109 connected to intra-frequency neighboringcells can receive the relevant information without gaps in receptionform their primary cell and with minimum additional complexity. There anumerous examples of DL information of interest to UE 109 of neighboringcells. UE 109 while fully connected to a first cell may need to makemeasurements about neighboring cells to aid in fast handovers (HO) andcell selection/re-selection. These measurements may be very basic suchas received power levels and may require reading the synchronizationchannel (SCH). Specific system information in addition to the powerlevel measurements may be required for HOs such as system frame numbers(SFN). Below, we list how reading some system information and RACHresponses of a neighbor might be beneficial for a UE connected to acell.

UE 109 connected to a cell may receive some of the system parameters ofneighboring cells from the current cell itself. However, any parameterthat changes so frequently as to require regular monitoring is best readfrom the neighboring cell directly. Certain parameters/characteristicsof cell change with a known pattern. For example the SFN alwaysincreases sequentially with every sub-frame. However, in order to knowthe current or future values of such parameters, it is necessary for UE109 to synchronize with a base value by reading directly from theneighboring cell. Reading system information directly from theneighboring cell may be advantageous to reduce the overhead of reportingin the DL-SCH of the current cell.

The main reasons to read a neighbor cell's system information directlyin its DL are: the information changes very frequently; the UE 109 mustsynchronize with a current base value of a changing parameter; and it isadvantageous to save the overhead of individually transmitting systeminformation to every UE 109 via the current cell. Some parameters thatare advantageously read from the DL transmissions of system informationare SFN, power control parameters and RACH parameters. Some of these maybe included in primary-BCCH (P-BCCH) and transmitted in the BCH. Atleast a few of these parameters may also be transmitted in blocks in adynamic-BCH (D-BCH). The D-BCH is expected to be transmitted inscheduling units (SUs) with different frequencies. There are a number ofmost important parameters that, if read before disconnecting from thesource cell and transmitted in D-BCH blocks, may help reduce latencies.These include: power control parameters in support of inter-cell powercontrol; UL interference if not in the P-BCCH; DL reference signal (RS)transmitted (Tx) power at the neighboring cell for pathloss estimation;load indicator; and the power (Target SINR) gap between serving andnon-serving UEs 109. If UL interference, DL reference signal (RS) Txpower and Target SINR are not needed independently but only in thecontext of an open loop power control algorithm, then they can be moreefficiently communication via a single parameter, the common powerbaseline defined as the sum of these parameters.

RACH parameters of neighboring cells are only needed in the context of aHO. It is assumed that static parameters, such as Zadoff-Chu sequences,location of random access opportunities and low rate varying powercontrol parameters, are forwarded to UE 109 by the serving cell alongwith the HO command or the HO indication in case of early RACH access.The only fast varying power control parameter the UE 109 would need toread on the D-BCH is the UL interference, if it not in the P-BCCH likethe SFN. These parameters are likely to be transmitted with the highestfrequency for any of the D-BCH blocks. These parameters can all bebunched together and transmitted in one SU with identical frequencies.Note that a D-BCCH block is transmitted in the DL-SCH.

It might be beneficial for UE 109 to receive RACH responses of message 2and message 4 from neighboring cells while still connected to the sourcecell. This permits UE 109 to initiate a RACH access in a neighboringcell without any gaps in the DL reception in the source cell. A RACHaccess may be initiated to receive timing advance for initiating ormaintaining UL synchronization. UL synchronization latencies may bereduced during HO using a RACH access in a neighboring cell withoutdisconnecting from the current cell. UE 109 may or may not be requiredto initiate RACH accesses in a neighboring cell without disconnecting orcausing gaps from the current cell. The protocol may be specified topermit building a UE that can accomplish this without adverselyaffecting performance. Messages 2 and 4 in the DL RACH responsescomplete the contention based aspect of RACH. These are thus candidatesto be read by UEs in neighboring cells before disconnecting from theircurrent cell.

As noted above there are various different types of information that maybe of interest to UE 109 in a neighboring cell. This information islikely to be contained in the SCH, BCH or certain blocks in DL-SCH. Inorder to read these, the UE also needs to be able to read the L1-L2control channel. This invention includes formats and structure so thatthe UE may receive these signals while fully connected to another cellwith minimal implementation overhead.

BCH and SCH are generally confined to a bandwidth of 1.25 MHz. Thisinvention does not propose any additional structure or restrictions tothese signals. In order to receive these signals while being fullyconnected to another cell, UE 109 must include additional basebandcircuitry that supports the reception of at least a 1.25 MHz duplicatetransmission within the same frequency band as the current cellfrequency.

The L1-L2 control channel is of interest because it carries allocationfor blocks on the DL-SCH. One block of D-BCCH and RACH responses formessage 2 and 4 are useful DL-SCH blocks for UE 109 in a neighboringcell to read. In order to read the L1-L2 control channel for allocationsfor these blocks without added implementation overhead, theseallocations are limited to sub-carriers that do not span more than 1.25MHz. The L1-L2 control channel is expected to span the entire bandwidthof the cell, and within the first few OFDM symbols of the sub-frame. Theallocations are also separately coded. While the control channel for aspecific allocation may be limited to sub-carriers spanning less than1.25 MHz bandwidth, it may still be necessary to decode the entirebandwidth to look for the allocation. This invention includes thefollowing to aid in the limiting the decoding to 1.25 MHz. The L1-L2control channel or equivalently the allocation for the first D-BCCHblock is in the first control channel in the overall L1-L2 controlchannel. The allocation for the RACH messages 2 and 4 is the foremost inthe L1-L2 control channel except if an allocation for the first D-BCCHblock is present in the same sub-frame. In this case the D-BCCH block isthe foremost allocation. Any other DL-SCH blocks that may be read by UEsin neighboring cells are also allocated in the foremost L1-L2 controlchannels. This allocation restricts the look up and decoding requirementto find the allocation for DL-SCH blocks that carry the information. IfUE 109 can decode up to 1.25 MHz of bandwidth in a neighboring cellwithout gaps, then it can be designed to read the L1-L2 allocationsabove.

The first D-BCCH block of system information and RACH responses ofmessages 2 and 4 are carried in DL-SCH. These signals may be of interestto UEs connected in neighboring cells. In accordance with this inventionthe UE is capable of decoding up to 1.25 MHz of continuous ordiscontinuous sub-carriers in a neighboring cell in addition to theregular transceiver capability. In order that the UE is capable ofreading the relevant DL-SCH blocks, these blocks are restricted to abandwidth of 1.25 MHz in this invention.

Note that the restriction of 1.25 MHz is related to the already existinglimit to the bandspread of the BCH. This restriction only applies to thebandwidth and does not restrict the center frequency of the allocation.It would be advantageous for a UE to be able to decode the BCH in theneighboring cell including decoding all relevant information from theneighboring cell with minimal additional implementation overhead. Therequired overhead is the additional circuitry required in the UE. Theabove design facilitates this capability.

In this invention contribution, the E-UTRA protocol is limited so that aUE connected in a current cell can decode some of the transmissions fromneighboring cells without gaps and with minimum implementationcomplexity. In this invention: the synchronization channel and BCH arelimited to a bandwidth of 1.25 MHz; the first block in D-BCH and RACHresponse messages 2 and 4 are transmitted in the limited bandwidth of1.25 MHz; and the first D-BCH block and the RACH responses separatelyencode the allocations. These acceptable portions are included in theE-UTRA TS.

FIG. 5 is a flow chart illustrating operation of this invention. Node A501 transmits on the primary base station 101 on the primary channel andincludes normal two-way voice and data operations. This is expected tobe a synchronous operation. Node B 501 of a neighboring cell such asbase station 102 and transmits the secondary data described above.Transmission of these blocks is restricted to a bandwidth of 1.25 MHz asdescribed above. This is expected to be a one-way transmission from basestation 102 to UE 109 only and occur on a non-synchronous channel. Userequipment reception 503 occurs at the UE 109 using a primary and asecondary baseband channel as described above and further detailedbelow. User equipment reception 503 supplies data to primary channelutilization 504 and secondary channel utilization 505. FIG. 5illustrates a return path from primary channel utilization 504 to node Avia user equipment transmission 506.

FIG. 6 is a simplified block diagram of user equipment 109 adaptedaccording to this invention. Radio transmission and reception occur viaantenna 601 and radio frequency transceiver 602. Radio frequencytransceiver 602 in is two-way communication with primary basebandprocessing 610. Primary baseband processing 610 supports the normalvoice and data transmissions. Primary baseband processing 610 is intwo-way communication with control circuit 620. Also coupled to controlcircuit 620 are handset 621 including a microphone and earphone as knownin the art, display 622 and keypad 623 accommodating user input. Radiofrequency transceiver 602 also supplied secondary baseband processing615. As described above, secondary baseband processing 615 processes thedata received from neighboring cells. Control circuit 620 uses thissecondary data as described above. Secondary baseband processing 615 issimpler than primary baseband processing 510 due to the restrictions onthe transmission character.

1. A method periodically broadcasting system information of radiofrequency communication between a user equipment and a plurality of basestations, comprising the steps of: periodically broadcasting systeminformation by each base stations about a cell served by the basestation; receiving at the user equipment said broadcast information froma primary base station serving the cell including the user equipment;and receiving at the user equipment said broadcast information from asecondary base station other than the primary base station.
 2. Themethod of claim 1, further comprising: communicating primary databetween the primary base station and the user equipment using a primaryfrequency sub-band having a first bandwidth; wherein said step ofperiodically broadcasting system information includes transmitting usinga secondary frequency sub-band having a second bandwidth less than thefirst bandwidth; and wherein said step of receiving at the userequipment uses simplified baseband processing relative to said step ofcommunicating between the user equipment and the primary base station.3. The method of claim 2, wherein: said primary data includes two-wayvoice data.
 4. The method of claim 2, wherein: said second bandwidth is1.25 MHz.
 5. The method of claim 2, wherein: said step of transmittingdata at the secondary base station using a restricted frequency bandincludes transmitting random access channel parameters.
 6. The method ofclaim 2, wherein: said step of transmitting data at the secondary basestation using a restricted frequency band includes transmitting systemnumbers.
 7. The method of claim 2, wherein: said step of transmittingdata at the secondary base station using a restricted frequency bandincludes transmitting power control parameters.
 8. The method of claim6, wherein: said power control parameters include reference signal (RS)transmission power at the secondary base station for pathlossestimation.
 9. The method of claim 6, wherein: said power controlparameters include load indicator.
 10. The method of claim 6, wherein:said power control parameters include a power signal to noise ratio gapbetween serving and non-serving user equipment.
 11. The method of claim1, wherein: said step of communicating between the secondary basestation and the user equipment includes transmitting data at thesecondary base station in scheduling units with different frequencies.12. The method of claim 1, wherein: said step of communicating betweenthe secondary base station and the user equipment includes using datafrom said secondary base station at the user equipment to coordinatehandoff of the user equipment from the primary base station to thesecondary base station.
 13. A method periodically broadcasting systeminformation of radio frequency communication between user equipment anda plurality of base stations, comprising the steps of: communicatingbetween a primary base station and the user equipment via a two-waysynchronized channel; and communicating between at least one secondarybase station differing from the primary base station and the userequipment via a one-way non-synchronized channel.
 14. A user equipmentfor radio frequency communication between a user equipment and aplurality of base stations, comprising: an antenna; a radio frequencytransceiver connected to said antenna; a primary baseband processorconnected to said radio frequency transceiver for two-way communicationwith a primary base station; a secondary baseband processor connected tosaid radio frequency transceiver for one-way communication with at leastone secondary base station differing from the primary base station; anda control circuit connected to said primary baseband processor and saidsecondary baseband processor for control of said communication.
 15. Theuser equipment of claim 14, wherein: said secondary baseband processorhas simplified processing capability relative to said primary basebandprocessor.
 16. The user equipment of claim 15, wherein: said secondarybaseband processor can process a limited bandwidth relative to saidprimary baseband processor.